Frederick Williams Double barrel Question

Hi folks...I need some help on markings on this double barrel Frederick Williams Birmingham shotgun im purchasing next week. I know NOTHING about these stamps and the research i have done im assuming dates it between 1887 and 1925. The owner has shot modern shells thru it without a problem but discovered tonight he doesn't believe its actually nitro proofed and sent me what he thinks it might be. Im posting some pics if someone could help me. Gun is in full working safe order and NOT Damascus..twist or laminated steel but regular steel barrels

Look at these examples:
Proof Marks dating your gun : Vintage Gunshttps://www.milsurps.com/moz-extensi...rGoodImage.png

Yours is very similar, but lacks the wording
So it is NOT nitro-proofed.
A nitro-proofed gun would bear either "NITRO PROOFED" in clear text or a proof mark with NP.

Well....its fully restored...dunked in acid and pattern slightly back and i found out it is twist steel, Didn't go too long in acid / bluing method only 4 x and im happy. Gun turned out very well....i am still knocking it down to either 20 or 16 gauge haven't decided. Obviously the shiny barrel was polished to bare steel and the blued barrel had acid done and pattern brought back.